Coolant Level - Reservoir vs. Filler Neck

[TurboLag23]

Hey all!

Just installed a Jackson Racing DROC on my BRZ, and I had a question regarding coolant levels.

I followed the refill procedure laid out in the FSM, and have since run the car for 2-3 heat cycles. Coolant temperatures in low-speed/low airflow driving (first-gear around the neighborhood at <2500 RPM) usually hover around 90C once engine is fully warmed up, jumping as high as 95C when car is idling. Every time I check coolant level (next day, after motor has fully cooled!), the reservoir is always hovering around the "Max" line but the filler neck is always empty. I have been adding coolant to the filler neck every time (takes a few oz to fill to top of filler neck), but this cycle continues to repeat - and I'm worried I may be very slowly and methodically overfilling the car with coolant

Is this normal behavior for this cooling setup, for the reservoir to be full but the filler neck to be empty?

Thanks!

[Ultramaroon]

Service manual defines a procedure to eliminate air from the system. You are either gradually eliminating the air, or you have a leak. Can you smell coolant? Doesn't make sense for it not to pull from the reservoir when it cools.

[terboboost]

You can not overfill the engine with coolant. As said above, your either slowly getting the air bubbles out (this can be a long process) or you have a leak.

[TurboLag23]

Originally Posted by Ultramaroon

Service manual defines a procedure to eliminate air from the system. You are either gradually eliminating the air, or you have a leak. Can you smell coolant? Doesn't make sense for it not to pull from the reservoir when it cools.

So to clarify - when engine is running, coolant level rises maybe 1/2" above full line. Then when cooled, it drops about 1/2" under full line. So it is definitely pushing/pulling from reservoir with heat cycles - just not enough to fill to top of filler neck on the cooldown.

I smell coolant faintly (99% sure it's because I've invariably spilled a couple drops every time I top it off ), but I can't see any leaks/residue on any of the hoses or the radiator core itself. If this is just persistent/stuck air bubbles, I'm content to keep checking & filling or redo the burp procedure - just didn't know if it was a normal thing (forgot to note before draining OEM radiator prior to install).

[Ultramaroon]

In the end, there should be no air under the cap at the top of the radiator. If after several driving cycles, the radiator continues to accumulate air under the cap, something is wrong.

[KillerBMotorsport]

By the sounds of it, you're almost full. Or maybe there is a leak?

For now, let's say it's just slowly burping air. This is very common, and your temps are nowhere near dangerous, so don't sweat it yet. At this point I personally just keep an eye on the overflow. Top it off as needed, and when you notice the level is no longer dropping, you're good. If it does continue to drop, say more than 5 times of topping it off, you may have another issue.